Classic Grip
The classic grip for a watercolor paint brush is similar to holding a pencil. The only difference is that your index finger and thumb will grasp the handle above the ferrel (the metal thingy), about one-third of the way back from the bristles.

This grip will allow the brush to feel balanced in your hand, and provide you with the greatest control. It is great for big shapes that are painted with the arm and wrist, and for smaller details that are guided with the fingers.

Splatter Grip
The splatter grip requires you to grasp the middle of the brush with your thumb, and second and third fingers. To throw the paint, you may flick the brush or tap it against the index finger on your other hand. This technique will add some colorful and spontaneous effects to your artwork.